TDP-43 is the principal component of ubiquitin-positive inclusions in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). Mutations in the gene encoding TDP-43 have been identified in ALS and FTLD with or without motor neuron disease, providing a direct link between TDP-43 and neurodegeneration. Of note, TDP-43 pathology is observed to varying degrees in other neurodegenerative disorders. For instance, TDP-43 inclusions are present in up to 56% of Alzheimer's disease (AD) cases. As with ALS and FTLD-U, the cytosolic deposition of TDP-43 in AD is associated with the presence of abnormally phosphorylated TDP-43 (pTDP-43) and C-terminal TDP-43 fragments (cTDP). Compared to AD patients without TDP-43 pathology, those with TDP-43 pathology are cognitively and functionally worse, suggesting that abnormal TDP-43 causes a modified AD phenotype. Therapeutics that target TDP-43 may thus prove beneficial for this subset of AD patients in addition to ALS and FTLD-U patients. As treatments are investigated, it is essential to prepare for diagnostic issues that will arise when compounds are ready for clinical trials. In the evaluation of new treatments for ALS, FTLD-U and AD, it would be advantageous to be able to distinguish between patients with and without TDP-43 pathology. Thus, the development of antemortem assays that recognize TDP-43 proteinopathies is greatly needed. Moreover, the refinement of biomarker assays is a key strategy, not only for aiding with diagnosis of disease, but also for generating more sensitive measures of disease activity and progression. We hypothesize that the presence of TDP-43-positive inclusions in ALS, FTLD-U and AD suggests that TDP-43 levels in cerebrospinal fluid (CSF) and plasma will parallel TDP-43 brain pathology. Moreover, we believe that the sensitivity and utility of TDP-43 as a biomarker may be enhanced by developing enzyme-linked immunosorbent assays (ELISAs) that detect pathological forms of TDP-43, such as pTDP-43 and cTDP. Therefore, we generated polyclonal antibodies towards pTDP-43 and cTDP and propose to produce similar monoclonal antibodies, as these are critical for the development of reproducible assays with future clinical applications. Using our novel antibodies, we aim to develop sensitive ELISAs for the detection of total and pathological TDP-43 which will be used, together with immunohistochemical analysis of brain TDP-43 pathology, to assess whether pathologically modified TDP-43 in CSF and/or plasma is a reliable indicator of brain TDP-43 pathology in ALS, FTLD-U and AD. Importantly, given that longitudinal data is very limited, we will use both plasma and CSF collected longitudinally from ALS patients to examine pathological TDP-43 levels in relation to clinical presentation and rate of disease progression. PUBLIC HEALTH RELEVANCE: The refinement of biomarkers is a key strategy for elucidating the pathogenesis of neurodegenerative diseases and for developing sensitive measures of disease activity and progression. Overall, the goals of this project are to generate sensitive assays to measure pathologically modified TDP-43 in biological fluids and to validate their use as an urgently needed tool for diagnosing and monitoring the progression of TDP-43 proteinopathies, like amyotrophic lateral sclerosis, frontotemporal dementia with ubiquitin-positive inclusions and Alzheimer's disease cases having TDP-43 pathology. Ultimately, such antemortem assays will provide a molecular basis for improving the early diagnosis of TDP-43 proteinopathies, which is important for the correct clinical management of patients, as well as provide a more efficient and objective evaluation of experimental therapies in clinical trials.